The circadian rhythm of melatonin in hypothyroidism and hyperthyroidism

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Abstract
In order to determine the influence of thyroid function on the pineal gland in humans, the circadian rhythm of the serum melatonin concentration was estimated in 16 women with thyroid disorders: 8 with hypothyroidism and 8 with hyperthyroidism, as well as in 5 healthy controls. A significant melatonin circadian rhythm was observed in all the three groups studied. The melatonin rhythm parameters derived from cosinor analysis: mesor (controls: 0.163 ± 0.03 nmol/l (± sem), hypothyroid patients: 0.176 ± 0.22 nmol/l, and hyperthyroid patients: 0.167 ± 0.04 nmol), amplitude (0.155, 0.145 and 0.138 nmol/l, respectively), acrophase (1:38, 2:22 and 1:51 h, respectively) did not differ significantly in the three groups studied. Integrated 24-h melatonin secretion was also similar in patients and controls. The melatonin concentrations were positively correlated with TSH levels in hypothyroidism, and negatively correlated with T3 in hyperthyroidism. In conclusion: in patients with hypo- and hyperthyroidism the circadian rhythm of melatonin secretion is not altered.